A device for adjusting the stiffness of a suspension spring includes a locking sleeve which defines a helical slot for accepting one end of the suspension spring, and an adjusting ring mounted with the ability to rotate relative to the locking sleeve about a main axis. The adjusting ring has a finger which emerges into the helical slot and is able to form an end stop for the end of the suspension spring. Structure is provided for locking the rotational mobility of the adjusting ring relative to the locking sleeve.

A suspension system has a spring which may be prevented from being completely withdrawn and separated from a spring pad even in a situation in which an additional rebound further occurs in a full-rebound state and the spring deviates from a range (a free height of the spring) in which the spring can be extended.